Titan3 g2 s tem

WS₂ triangles grown on the SiO₂ substrate were transferred to a QUANTIFOIL gold TEM grid. Poly(methyl methacrylate) (PMMA) was spin-coated onto WS₂ triangles as a supporting film during transfer. The SiO₂ layer was etched away by soaking the substrate in 1 M sodium hydroxide (NaOH) aqueous solution; the PMMA/WS₂ triangle film was cleaned using distilled water several times, followed by fishing out of the film with the QUANTIFOIL grid. After the film was completely dried, the PMMA layer was cleaned using acetone and isopropanol. STEM was carried out by FEI Titan3 G2 S/TEM operating at 80 keV. To reduce irradiation damage, we kept the beam current below 40 pA. A high-angle ADF (HAADF) detector was used for STEM-ADF imaging. To enhance the contrast from sulfur atoms to ensure accurate counting of monosulfur vacancies, we used a LAADF condition rather than a HAADF condition. For most images in the text, a Gaussian blur filter was applied by the ImageJ program to reduce noise and enhance the visibility of structural details, but raw images were used to acquire line profiles of ADF intensity. STEM-ADF image simulation was conducted by the QSTEM package (49 ). Simulation parameters, such as acceleration voltage, spherical aberration (C₃ and C₅), and convergence angle and inner/outer angle for the HAADF detector, were set according to the experimental conditions.